The present invention relates to a photon receptor, which may be configured to detect a single photon.
There is a need for a photon receptor that is capable of detecting a single photon. Single photon detection is also useful as a low level light detection means for spectroscopy, medical imaging, military applications or astronomy. An optimum signal to noise ratio is achieved when a photon wave is detected by an array of photon receptors, as the noise is then limited by the shot noise and is independent of noise.
Single photon receptors are available in the form of photo multiplier tubes (PMT) and single photon avalanche photo diodes (SPAD). PMTs have the disadvantage of having low quantum efficiency, being expensive, bulky, mechanically fragile, and requiring high biasing voltages and cooling. They can also be damaged and can require a long settling time after exposure to high light levels or stray magnetic fields. On the other hand, SPADs have the disadvantage of having a relatively low gain and high dark count rates, especially when operated at higher repetition rates. They are also expensive and require high bias voltages and external cooling.
Prior methods of providing a single photon detection threshold photodetector are described in U.S. Pat. Nos. 6,720,589 and 6,885,023, which are incorporated herein by reference. U.S. Pat. No. 6,885,023 (to Shields , et al., issued Apr. 26, 2005) discloses an optical device and a method of making an optical device, such as a radiation detector or an optically activated memory, that includes a barrier region located between two active regions. One or more quantum dots are provided such that a change in the charging state of the quantum dot or dots affects the flow of current through the barrier region. The charging states of the quantum dots are changed by an optical device.
U.S. Pat. No. 6,720,589 (also to Shields, issued Apr. 13, 2004) discloses a semiconductor device, which can be configured as optically activated memories or single photon detectors. The devices comprise an active layer with a plurality of quantum dots and an active layer. The devices are configured so that charge stored in the quantum dots affects the transport and/or optical characteristics etc of the active layer. Hence, measuring such a characteristic of the active layer allows variations in the carrier occupancy of the quantum dots to be determined
The devices of the '023 and '589 patents generally require fabricating devices having one or more sheets of semiconductor quantum dots buried within another thin film layer, and generally comprising 4 to 8 total layers to form an active device. As the fabrication of multiple thin films and active semiconductor layers in the structure suggested in the above patents poses technical challenges that generally decrease yield and increase manufacturing cost.